Previously, curing compositions composed of polymers, particularly polysulfide polymers, having two or more thiol groups per molecule and metal oxidizing agents, e.g., PbO2 or MnO2, have excellent barrier properties against water vapor and gases, excellent adhesion, and excellent weather resistance, and in addition, have sufficient strength. Therefore, the curing compositions have been used over the years as sealants for construction, civil engineering, automobiles, aircraft, or the like, sealants for insulating glass manufacture, adhesives, or coating compounds.
In particular, with respect to sealants for insulating glass manufacture, as described in Japanese Unexamined Patent Application Publication No. 9-217008, etc., the above-described curing compositions have a strength at break of 100 to 200 N/cm2 in terms of properties and satisfactory gas-barrier properties as well, and therefore, are widely used in sections, e.g., sealants for insulating glass manufacture, required to have sufficient strength and gas-barrier properties.
Curing compositions composed of polymers having two or more thiol groups per molecule and compounds having two or more isocyanate groups per molecule have satisfactory dynamic durability. Furthermore, similarly to curing compositions composed of the polymers having two or more thiol groups per molecule and the metal oxidizing agents, even when cured compounds are exposed to the outdoors over an extended time period after being applied, the surfaces of the cured compounds are not stained, so that excellent anti-staining properties are exhibited and, in addition, excellent adhesion is also exhibited. The curing compositions composed of polymers having two or more thiol groups per molecule and compounds having two or more isocyanate groups per molecule are used as polysulfide-based sealants composed of thiol-containing polysulfide polymers and polyisocyanate compounds, and are used as sealants for construction, civil engineering, etc., adhesives, or coating compounds. Since the curing compositions composed of polymers having two or more thiol groups per molecule and compounds having two or more isocyanate groups per molecule include no metal oxidizing agent and, therefore, are environmentally friendly, the replacement of metal oxidizing agent curing system has become rapidly widespread in recent years.
However, when polysulfide-based sealants based on polyisocyanate compounds are used as sealants for insulating glass manufacture, vehicle window frames, etc., with the same formulation as in the curing compositions based on the metal oxidizing agents, the strength at break and the hardness of the cured compounds are low and, therefore, the resulting cured compounds simply have unsatisfactory properties. Furthermore, polysulfide-based sealants based on polyisocyanate compounds have poor gas-barrier properties. It is known that carbon black is used as a reinforcing material to improve the hardness of the polysulfide-based sealants. When the amount of carbon black used as a reinforcing material is increased, the strength at break is improved. However, there are problems in that the storage stability of base compound is significantly deteriorated and the workability after storage of the base compound is also deteriorated.